Quenching of metals



Patented Feb. 1, 1944 UNITED STATES PATENT OFFICE q .ounucniiri firrmrsns I I Cliflord G. zur Horst, Hampton Township, Al-

lcgheny County, Blaine B. Wescott, Churchill Borough, and Leslie W. Yollmer, Pittsburgh, Pa., assignors to Gui! Research 8: Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing.

O al

1942, Serial N 426,537. Dividedam'i this application July 13, 1943, Serial No. 494,532

6 Claims. (curls-13.1)

heating the metal to'atemperature above its critical temperature and cooling the metal by immersion in a quenching oil bath comprising a ht minual quenching oil and 1.0 to 20.0 per cent of a cumarone-indene resin; all as more fully hereinafter set forth and as claimed.

While our-invention is useful in the quenching of any metal which is advantageously quenched in an oil bath having a high initial quenching speed, it is particularly useful in the quenching of iron base alloys and it will be described hereinafter in detail in connection with the quenching of steel.

Many. metal alloys, particularly iron base alloys, such as carbon steels "and alloy steels, require heat treatment for the development of maximum properties of hardness and strength. These properties are dependent upon the establishment of certain physical structures in the metallic components or the alloy. In steel, hardenability is determined by the extent to which a. martensitic structure is established in the alloy. The production of this structure in steel is usu- Quenching in aqueous quenching media deveh ops the properties of strength and hardness to the maximum obtainable. for a given section of metal. However, quenchingin aqueous quenching media is undesirable in many cases because these media tend to set up excessive amounts of internal stress in the steel resulting in distor tion and warping and, in the extreme case, crack-- ing of. the quenched piece. As a result, aqueous quenching media have been'supplanted by mineral oil quenching media where such mineral oil quenching media have sufiiciently high quenching speeds vto produce the desired properties in the quenched metal because such mineral oil quenching media are particularly adapted-to internal stresses and distortion in the quenched product. This results from the fact that the quenching speeds of mineral oilquenching media are substantially slower than those of aqueous quenching media, due to considerable extent to the formation of a mor or less persistent vapor envelop about the quenched piece at the beginning oi" the quenching cycle, and'the fact that in the later stages of the quenching cycle the quenching speeds of mineral oil quenching media are sufliciently slow so that the internal stresses developed in the metal in the early stages of the cycle tend to be relieved.

ally accomplished by arresting at the desired;

point, the changes in the internal structure or the alloy which take place during the cooling of the steel from high temperatures.- The fact that desired point by suitable quick Quenching of the steel in aqueous or oil quenching baths'is generally used to arrest these then followed by a tempering treatment involving heating at relatively low temperatures to impart the desired ductility or toughness to the-- metal at some sacrifice in hardness. v

However, since the overall cooling. efllciency of the mineral oil quenching media heretofore known is not as great as that of aqueous quenching media, it has been difllcult or impossible to nefiect in mineral oil quenching baths quenching of pieces formed of steels having high critical cooling rates, sufliciently rapidly to develop the properties of strength and hardness to their maxi,- mum values or the quenching of pieces having high mass to surface ratios suiliciently rapidly to develop the properties of hardness and strength to the maximum depth.

It is desirable, therefore, to improve the quenching of metals in mineral oil quenching mediasothatthecoollngefllciencyintheearly stages of the quenching cycle is increased to more nearly approach the cooling efliciency of aqueous quenching media without increasing the quenching speed inthe later stages 01 the cycle sumciently to deleteriously afl'ect' the normal It is an object achieved by the present invention to provide a method of quenching metals, particularly iron base alloys, in mineral oil quenching media having initial quenching speeds greater than the mineral oil quenching media heretofore known.

It is a further object achieved by the present invention to provide mineral oil quenching compositions having cooling efliciencies more nearly approaching the cooling efficiency of water while retaining the stress-preventing characteristics of oil quenches.

The critical cooling rate of a metal is defined as the lowest cooling rate at which maximum hardness is developed. For steel the critical cooling rate is the lowest cooling rate which will produce a full martensitic structure in the steel. Thus it is generally most desirable to effect initial quenching at a speed sufllcient to produce a cooling rate at least equal to the critical cooling rate for as great a depth in the metal as possible and to effect the quenching with a minimum of distortion.

The cooling efficiency of a quenching medium is customarily defined in terms of quenching speed and the initial five second quenching speed is a convenient measure of this property of quenching oil compositions, and is the property with which this invention is most concerned. The initial five second quenching speed of a quenching oil composition as referred to throughout this specification and in the appended claims is determined according to the following formula:

Per cent available heat X100- removed in first five seconds Temperature rise in 5 sec. test Temperature rise in cold quench test in which the respective values are measured as follows:

Cylindrical test pieces one inch in diameter and 2.5 inches long of stainless steel containing about 18.0 percent of chromium and 8.0 per cent nickel are heated for one hour at 1500 F. in a furnace equiped with an automatic temperature control. Two quarts of the quenching oil composition to be tested are placed in a calorimeter which has a wire screen positioned in the center of the oil .bath to insure constant depth of immersion of the samples. The quenching composition is heated to an initial temperature of 100 F.

One of the preheated test pieces is immersed mineral quenching oils does not deleteriously affeet the stress-relieving properties which normally characterize such oils. By quenching pieces formed of metals having high critical cooling rates or pieces difficult to quench because of a high ratio of mass to surface, by immersion in in the quenching bath by means of light tongs for a period of five seconds without agitation. The test piece is then removed and the bath agitated and the maximum temperature reached is measured. A second preheated test piece is immersed in the bath at an initial temperature of 100 F. and the bath is agitated until the maximum rise in temperature has been produced. The maximum temperature rise measured in this cold quench represents the available heat of the test piece. By substituting the values thus determined for the five second quench and for the cold quench in the above formula, a measure of the heat removed in the first five seconds as compared with the total available heat is obtained and is referred to herein as the initial five second quenching speed.

We have discovered'that oil-soluble cumarone-indene resins have the property, when incorporated in a light mineral oil such as has been used heretofore in the. quenching of metals, of substantially increasing the initial five second (ill quenching oil compositions containing these cumarone-indene resins, cooling of the metal can be effected at a rate more nearly approaching or equal to the critical cooling rate of the metal without creating excessive stresses in the metal. In this way the hardness of metal having high critical cooling rates can be developed to a degree heretofore unattainable with mineral oil quenching media, and hardening can be effected to a greater depth in pieces having high ratios of mass to surface. Both of these results can be achieved with a minimum of distortion.

The cumarone-indene resins which have been found useful for the purpose of our invention are customarily prepared commercially by the polymerization of the cumarone and indene components of coal-tar naphtha fractions. The starting material is usually a sharply fractionated naphtha boiling between and C., which has been treated for the removal of such impurities as naphthalene and phenols. Va'rious polymerization catalysts may be used such as sulfuric acid, stannic chloride and anhydrous phosphoric acid. However, in substantially all commercial operations sulfuric acid is used in amounts corresponding to about 0.2 to 1.0 per cent by volume of 66 B. acid. The polymerization is highly exothermic and the batch should be kept below about 20 C. usually at 0 to 15 C. Dilution of the naphtha with petroleum distillate'is sometimes resorted to in order to minimize overheating. The use of petroleum distillate in this manner also has the advantage that it has a solvent action on the desired polymerized products while undesirable products are caused to precipitate.

I When petroleum distillates are not present during the polymerization, they may be used to effect a separation of the polymerization products by dissolving out the resin polymer. After polymerization, tar and acid are settled out of the oil containing the cumarone-indene resin and the oil is neutralized with dilute caustic soda solution and is washed with water. The washed oil is then distilled oif and the resin is recovered as a residue.

The properties of cumarone-indene resins can be varied by producing modified resins, for example such as are formed in the presence of alkyl ethers, phenols and the like. Properties can also be modified by formation of hydrogenated cumarone-indene resins. All of these cumaroneindene resin products have the property we have found of increasing the initial five second quenching speed of mineral oils and by the term cumarone-indene resins as used herein and in the appended claims we mean to include not only the resins which are obtained by the polymerization of cumarone and indene but also the modilied and hydrogenated cumarone-indene resins.

Among the cumarone-indene resins with which we have obtained good results according to this assoase invention are resins exhibiting the following properties: Table 'O-IresinA I O-IreeinB Melting range .-G 1445-185 160 .-per 0. 1 0. 1 Acid number (max. 0.84 1.0 Ba cation num Not saponiiiable Not saponiiisble t i 3% 1.1a 5 lnbility.- Complete Complete I The cumarone-indene resins, when incor- P rated in amounts correspondins ito about 1.0

to 20.0 per cent by weight in mineral oils such as have been used heretofore in the. quenching of metals. produce quenching compositions having quenching speeds or at least about 20.0 per cent.

The various cumarone-indene resins contain plated by the present invention do not increase the initial rive second quenching speed of'a mineral oil in the same degree. some are more eflective than others and also some are more oilsoluble than others and may be used in larger amounts. We have found also that in most cases the effect of each cumarone-indene resin increases directly with the amount used up to a maximum and then decreases. Consequently, the

optimum range of concentration for diiferent cumarone-indene resins. will diifer. ln l neral. however, we have found that amounts between about. 1.0 and 20.0 per cent by weight eifect substantial increases in the initial five second quenching speed of an oil. By'use of the proper resin in suitable amount substantially any initial 5 second quenching speed between about 20.0 per cent and 37.0 per cent can be obtained. It is possible, therefore. by suitably compounding quenching oil compositions according to our invention to provide a quenching medium which has an ini-- tial five second quenching speed particularly adapted to.- give best results with the particular metal and the particular type of piece being quenched. For most P rp ses it is advantageous to use a quenching composition having an initial nve second quenchin speed of at least about 80.0 per cent and for this reason 'we flnd it most advantageous to use the cumarone-indene resins in amounts corresponding to at least about 3.0 per cent by weightofthe oil.

In compounding the quenching oil compositions or our invention we select for the quenching bath a mineral oil of the type customarily used for quenching steel and other metals and these oils are referred to herein asmineral quenching E specifically several of the more advantageous quenching compositions oi our. invention is usually carried out by immersion of the preheated metal'in the quenching oil composition until sumcient heat has been removed to reduce its temperature the desired amount. The quenching oil may be used repeatedly with only slight deterioration.

In the following examples there are illustrated forms of our invention and the results obtainable scampze 1.-.-'rne following test results iIIustrate the use oi cumarone-indene resins according to our invention.

A series of quenching oil compositions was prep red by mixing a hydrogenated cumarone-im .dene resin having the properties shown above in Quenching oil No.- 2-.

the table for resin A in amounts between 1.0 and 15.0 per cent by weight, respectively. with a neutral paraflinic mineral oil having a viscosity of I 100 S. U. S. at 100 F. The initial five 80001111 quenching speeds of the respective compositions were then measured as above described and the following results were obtained:

quenching speed Quenching oil+1.0% cumarone-resin A..- 20.18

, Quenching cil+2.0% cumarone-resin A--- 24.86

Quenching oil+3.0% cumarone-resin A 31.26 Quenching oil+4.0% cumarone-resin A 3320 Quenching oil+5.0% cumarone-resin -A..-.. 84.86

Quenching oil+7.5% cumarone-resin a--- sass Quenching-oil+10.0% cumarone-resin A-.. 38.81 Quenching oil+12.5% cumarone-resin A..- 86.83

Quenching oil+15.0% cumarone-resin A..- 36.31

As will be seen from these results, this hydrogenated cumaroneindene resin is a very eflectivequenching accelerating agent. Also, .it will be observed that the increase in initial iive second quenching speed with increased amounts of resin passes through a maximum. v

' Another series of quenching oil compositions was prepared'by mixing a cumarone-indene resin having the properties shown above in the table ior resin B, in amounts corresponding to 1.0 to 5.0 per cent by weight, respectively, with the same neutral parafllnic oil of 100 S. U. 8. at, 100

1!. The initial flve second i'iuenchii'iav speeds of the oil-resin compositions were determined as oils. The oils usedforthispurposemaybeeither naphthenic or paraillnlc oils andhre usually acid treated neutral oils having a viscosity of about to 200 S. U. V. at F., relatively high iiash and fire points, and substantial heat stability aiidresistance to sludging. For optimum results we have found that paraiiinic oils which usually quenching accelerating alentsof our invention outlined above. The results obtained are as follows:

1 Initial flve second quenching speed Quenching oil No. 2-..- 10.00 Quenching oil+1.0% cumarone-resin B--- 21.2 Quenching oil+2.0% cumarone-resin B--- 30.80 Quenching oil+8.0% cumarone-resin B--. 82.42 Quenching.oil+4.0% cumarone-resin B--- 35.01

Quenching oil+5.0% cumarone-resin B--- 35.81

These results also demonstrate the eilectiveness e of the cumarone-indene resins as quenching aecelerating agents.

Hardness and distortion tests were made on piecesof metal quenched in the oil composition containing 5.0 per cent 0! this cumarone-indene B. These measurements were made on specially designed pieces adapted to show. measurably. very small changes in shape due to distortion and having a continuously cha ains section which permitted measurement of the variation in surface hardenabili'ty-with varying section oi. the Y piece and thereby gives an indication oi the varimun "five ism-a 1 Change in Quenching medium D Illusion dimfinsion;

Tap water +0. 0134 +0. 0102 +0. 0116 ilNo.2 +0.(Xl32 +0.00% +0.0028 Oil No. 2 and 6% -1 resin B +0.0020 +0. 0041 +0.0041

Results of th hardness measurements are shown in the following table:

. Brinellhardness Quenching medium I Minimum Maximum Variation 649 723 74 Oil No. 2 361 690 335 Oil No. 2 and 0-1 resin 3.. 573 720 147 From these results it will be observed that while tap water gives the greatest surface hardness and a variation of only74 points from the hardest to the softest area, it also gives maximum distortion. The mineral oil alone minimizes distortion but gives a lowered surface hardening and a variation of 335 points from the hardest to the softest point. on the other hand, the specimen quenched according to our invention in a quenching oil composition having an initial five second quenchingspeed of about 35.8 per cent showed distortion approximately equal to that obtained with plain mineral oil, a' surface hardness almost equal to that obtained with water and a hardness variation little greater than that obtained with waterand substantially less than that obtained with oil alone, indicating adepth of hardening intermediate between those obtained with water and with oil alone, respectively.

- This application is a division of our copending parent application Serial No. 426,537, filed January 12, 1942.

While we have particularly described our inbodiments thereof, it is to be understood that it isnot limited to such specific embodiments except as. hereinafter defined in the appended claims. I

'What 'we claim is:

1. Animproved quenching oil composition comprising a mineral quenching oil and at least about 1.0 per cent by weight of an oil-soluble cumarone-indene'resin.' Y

2. An improved quenching oil composition comprising amineral quenching oil and an oilsoluble cu'maron-indene resin in controlled amount adequate to impart to said quenching oil an initial five. second quenching speed of at least about 20.0 per cent without substantially modifying the stress-reducing characteristics of the oil. a

I 3. A method of quenching metals comprising heating the metal to a temperature above its critical temperature and thereafter cooling the metal by immersion in a quenching oil bath comprising a mineral quenching oil and an amount of an oilsoluble cumarone-indene resin, above about 1.0

per cent adequateto impart to the quenching oil bath an initial flve second quenching speed of p at least about 20.0 per cent.

per cent without substantially modifying the stress-reducing characteristic of the oil.

6. A method of quenching metals comprising heating the metal to a temperature above its critical temperature and thereafter cooling the metal by immersion in a quenching oil bath comprising a mineral quenching oil and an amount of an oil-soluble cumarone-indene resin above about 3.0 per cent adequate to impart to the quenching oil bath an initial 5 second quenching speed between about 30.0 to 37.0 per cent.

CLIFFORD G. m HORST. BLAINE B. WESTCOT'I. LESLIE W. VOLLMER.

vention with reference to' certain specific em- 

